The ever-increasing reliance on information and the computing systems that produce, process, distribute, and maintain such information in its myriad forms continues to put great demands on techniques for data storage and data protection. As demands and expectations from an information network change over the lifetime of the information network, initial decisions made with regard to where and how data is stored in the information network may need to be altered. Modifying file systems in an information network can implicate not only a change of storage resources, but also personnel resources to implement such changes.
For example, should a storage administrator determine that information stored in multiple file systems would be more effectively accessed in a single file system, implementing such a modification could take many hours of equipment and personnel time. Such a modification could be implemented by backing up the file systems to be united, clearing storage objects storing the data of those file systems, uniting all the storage objects into a single set of volumes, and then restoring all the data of the various file systems onto the single set of volumes of storage objects.
Alternatively, a storage administrator could choose to provide various file systems through directory structure access points that disguise the distinction between the separate file systems. A disadvantage of such a system can be that free memory, or extent, space between the various file systems is not shared among the file systems, thereby potentially resulting in an inefficient distribution of resources.
It is therefore desirable to have a low cost method of encapsulating one or more file systems into a union of file systems. Low cost can be realized by having a method that does not involve a lengthy and resource intensive backup/restore. In other words, a method in which each directory entry for each file in a file system does not need to be modified or copied. Further, it is desired that such a method of encapsulating file systems results in the free space for each encapsulated file system being useable by all file systems in the union of file systems.